He came to the ER with chest pain, shortness of breath, and atrial fibrillation with a heart rate of almost 120 beats per minute. It wasn’t a heart attack, and it wasn’t some rare disease. He was emergently ill because his physician overreacted to blood tests, and prescribed a thyroid pill he didn’t need.

According to an article in JAMA Internal Medicine, the 72-year-old patient described above had gone to his doctor several months earlier, with mild, nonspecific physical complaints. The doctor ordered a blood test, which showed a slight elevation in his TSH, or “thyroid stimulating hormone.” TSH is the molecule your body releases when your thyroid isn’t producing enough hormone. When TSH is elevated, it can be a sign that your thyroid gland is underperforming.

In this patient’s case, even though his TSH level was high, the level of thyroid hormone was normal in his blood. That means his situation isn’t straightforward. Suppose his TSH had been elevated at the same time as his thyroid hormone was low. And suppose that he was also showing specific signs of thyroid problems—maybe he was cold all the time, or had a slowing of his heart rate. This constitution of signs and symptoms would be strongly suggestive of hypothyroidism—that extra TSH in his bloodstream might not be up to the task of prodding his thyroid to do its job. In that case, it would be reasonable for his primary care physician to prescribe thyroid hormone replacement, and see if he got better.

In this patient’s case, however, his blood tests weren’t straightforward. And his only symptoms of thyroid deficiency were non-specific, things like low energy, a complaint that I expect half the people reading this post are experiencing right now (in response to my engaging prose). When people’s blood tests are inconclusive, and their symptoms are non-specific, physicians need to be cautious about prescribing thyroid replacement.

Unfortunately, this patient’s doctor decided to prescribe thyroid medicine, thinking it would correct his blood work and give him more energy.

Physicians need to be more comfortable watching such patients before treating them, especially when they are elderly and their TSH levels are only slightly abnormal. As for patients who are diagnosed with subclinical hypothyroidism: they should remind their doctors that when it comes to thyroid replacement, sometimes less is more.

I am a physician and behavioral scientist at Duke University. My research and writing explores the quirks in human nature that influence our lives — the mixture of rational and irrational forces that affect our health, our happiness and the way our society functions. (What ...